Bragg filters/mirrors

There are three accessories used to produce monochromatic radiation metal foil filters, crystal monochromators, and focusing mirrors. An element with atomic number Z can be used as a selective filter for radiation produced by an element of atomic number Z+ 1. For example, a nickel (Z=28) absorption filter, may be used to cut out the Cu KjS (Z=29 for Cu) radiation, leaving only Cu Ka radiation.Not all white radiation, however, is eliminated by this method. Alternatively a single-crystal monochromator may be used. An intense Bragg reflection from the monochromator crystal is used as the incident beam for X-ray diffraction studies. Focusing mirrors, designed to produce a beam that is not only monochromatic but also convergent, may be used. In this case the incident beam is doubly deflected by two perpendicular mirrors. 

Fig. 1 Bragg mirror structure and spectra, (a) Schematic diagram of layers [a, b] repeating N times. Physical parameters depending on the porosity, P, are identified in the text, (b) Aeoustic transmission speetra for pSi Bragg mirror darker line experimental data, lighter line transfer matrix model), (c) Modeled and measured transmission data for pSi rugate filter, (b, c) (From Thomas et al. (2010) reprinted with permission Irom Applied physies letters by American Institute of Physies, Copyright (2010), American Physical Society)...

Figure 4.14. Typically the mirrors are fabricated using a Bragg dielectric stack consisting of multilayers of dielectrics with different indices of refraction, (high) and 2 (low), stacked alternately with high and low indices of refraction for several cycles. The thickness of each layer is chosen so that a quarter-wavelength of the light that is to be filtered fits in the gap ...

Lay out a tunable Fabry-Perot optical filter in a multiproject wafer process as shown in Figure 4.24. The top Bragg mirror should be composed of a stack of dielectric films and should be flat to within a fraction of a wavelength of light that will be filtered. 

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